Satin white pigment and process of making same



Patented Jan. 24, 1939 i UNITED STATES PATENT OFFiCE SATIN WHITE PIGMENT AND PROCESS OF MAKING SAME,

Lincoln T. Work, New York, N. Y.

No Drawing. pplication February 4, 1935,

Serial No. 4,988 g 3 Claims. (Cl. 13458) This invention relates to the production of a It is well known that acid will react with clay pigment, and is concerned more particularly with to extract alumina, thus producing aluminum sula white pigmentary composition containing satin phate solution and an altered clay. However, the white and a clay residue, which composition may value of that altered clay as a component of a 5 be obtained throughaseries of chemical reactions pigment composition has not, so far as I am 5 herein described. The invention involves also the aware, been mentioned in the prior art. process by which this composition is prepared. From the foregoing it is evident that the broad Satin white has been known for a great many aspects of the prior art on satin white preparation years. It is produced by the reaction of calcium are well known. The improvements herein dehydroxide with aluminum sulphate in aqueous scribed and claimed are largely specific in nature. solution. There appears to be considerable Having in mind the development of the prior debate as to the exact chemical identity of this art, it is an object of my invention to provide a material, but the present general tendency is to mixed p g pigment pos o C nsistaccept the theory that the said substance consists ing essentially of a clay substance or residue and essentially of tricalcium aluminate and calcium satin white. Another object of invention is the sulphate, both in hydrated form. The sulphoprovision of a pigme Composition Comprising aluminate compound identified in Portland cesatin white and chemically processed and altered ment as the reaction product of calcium alumiclay. A further object is to provide a process for nate and calcium sulphate is not stressed as a th pro 0f $11011 pigment pos o product of this reaction. Preformed satin white The above, a other, j s o invention are may be blended with calcium carbonate or whitattain d y practicing a p ss w generally ing, or it may be used alone, considered, comprises reacting a clay with sul- One of the principal uses of this material is in phuric acid in amount and concentration sufiicoating compositions for preparing coated paper. cient to convert at least the major proportion Of In preparing paper coating compositions therealumina content of the clay into aluminum sulfrom, sizing material is used with a paste of the phate, whereby an aluminum sulphate solution satin white. Among the more recent developand an insoluble sludge of clay residue are proments in the production of satin white paper duced, and reacting the solution with hydrated coating compositions are the uses of materials lime in the presence, or absence, of clay residue such as soaps, resin products, etc.,'which serve to sludge. A feature of the process is the precipitadisperse the satin white in the mixture. Some tion of satin white inv the presence of said clay of these wetting agents make it possible to dry residue sludge. According to the preferred emthe satin white crystals although heretofore they bodiment of my invention I use as starting mahave been handled as a thick paste. terial a suitable paper clay, preferably one which According to the prior art the reaction beis high in alumina content: this clay is treated tween aluminum sulphate and lime has been well with sulphuric acid to extract alumina, thereby known for a great many years. The recent deproducing a solution of aluminum sulphate. The veloments in the field of satin white manufacture solution may be, and preferably is, removed from have, for the most part, consisted in details .of the residual clay substance for purification, e. g., processing or treatment. For example, Ryan for freeing it from contained iron by the use of (U. S. Patent No. 1,470,765) produced the satin metallic aluminum. correspondingly, the clay white in a paste form and eliminated grit thereresidue may be treated with fresh acid to secure in by grinding the paste. Frederiksson (U. S. a maximum amount of aluminum sulphate solu- Patent No. 1,632,891) utilized basic aluminum sultion. Specific conditions for the reaction of the phate for reaction with hydrated lime, at room acid and the clay are well known, but for this temperature, to produce satin white as a thick purpose it is advisable to avoid the use of conpaste. He considered the basic sulphate essential centrated acid, as the latter has a tendency to in the creation of the crystal nuclei which deterchar organic material which may be present in mine the ultimate character of the satin white. the clay. It should be noted that sulphuric acid Lauderman (U. S.Patent No. 1,863,663) produced of moderate strength tends to decompose any a mixed pigment while utilizing a by-product of organic matter'present in the clay. After the calcium carbonate sludge from the caustic soda various steps are performed upon the solution and process. In this case excess lime was reacted the clay residue, the two are again mixed, and with alum toproduce the satin white in the preshydrated lime added as a precipitant for the ence of calcium carbonate. 7 satin white. 01', the solution may be purified, the

purified solution reacted with hydrated lime, and the resulting precipitate mixed with the clay residue.

The invention will be described more particularly with reference to the following example. 1 pound of clay of paper-coating grade is moistened with about 1 pound of water and .75 pound of H2804 monohydrate. The resulting mixture is held at a temperature of about 214 F. until the alumina content in the leaching mixture approaches the amount of available alumina of the clay, normally 20-30 percent. Assuming 25 percent alumina removed, the clay residue approximates .75 pound of special acid-treated mineral. The alum formed is approximately .85 pound. After the reaction is complete, the suspension is diluted to a slurry with water, and milk of lime slurry is added thereto to the extent of about 1.8 pounds of Ca(OH)2. 'Ihisyields'approximately 4 pounds of satin white pigment composition when due allowanceis made for the water of hydration in the compound; This pigmentcompositio'n maybe processed in paste form by the use of the'ball or'colloid mill, or by the use of dispersing agents. The-resulting product, with or without such processing, is suitable for use with casein as a coating for calendered papers.

The above process is of particular interest when treating clays which are relatively free of iron or other -'coloring constituents soluble with the aluminum, or when-such impurities are not objectionable in the product.

In carrying out this process 'on clay of normal I purity forpaper coating purposes, and. with the object of producing a pigment composition of particularly high whitenesa I prefer 'to separate the acid solution from'the cla'y'residue insoluble therein, and to purify the solution'by treating the same with metallic aluminum in quantity'sufiicient to remove therefrom iron and. other coloring ingredients dissolved 'from'the clay starting material. After this preferred step is practiced, the purified aluminum sulphate solution is returned to'the clay residue, whereupon tothe mixture is added that amount of hydrated lime necessary to effect the desired satin white reaction.

This invention offers two distinct advantages over present methods for the making of satin white pigment. First, the aluminum comes from a cheap source. By this process the'aluminum sulphate issecure'd'and 'purified in the solution without resort to the normal commercial procedure of crystallization. The avoidance of crystallization and the direct use of the solution represent an economy in the production of satin white. Second, the acid treatment of the clay leaves a residue improved in color through dissolution of iron and other coloring ingredients. Moreover, the-clay has undergone a desirable alteration'in structure through th'e extraction of the aluminum, which result makes the residue peculiarly advantageous because of its optical properties, the nature of its particle surfaces as a base for precipitation of satin white, and the desirable plastic properties imparted to the finished pigment composition.

The resulting satin white composition, accordingly, is a'white pigment having desirable properties from the standpoints of plasticity and solution, and reacting the so-purified solution I with hydrated lime in the presence of said clay residue.

2. Process which comprises treating finely divided iron-containing clay with sulphuric acidin an amount sufiicient to convert at least a part of the alumina of the clay to-aluminum sulphate, whereby there is produced a solution of aluminum sulphate containing iron sulphate and an acid-treated clay residue insoluble in said solution, separating the solution from the residue, treating the former with'a precipitant for iron and separating and discardingthe resulting iron precipitate, returning the soepurified aluminum sulphate solution to'the clay residue, and reacting therewith hydrated limein amount suiilcient to precipitate satin white in the presenceof particles 'of clay residue.

3. A pigment composition consisting essentially of finely divided particles of acid-treated clay residue and satin' white particles precipitated in the presence of said clay residueparticles.

' LINCOLN T. WORK. 

